Quantum mechanical modeling of electronic excitations in metal oxides: Magnesia as a prototype

► Characterizing excitations in metal oxides can provide insight into photocatalysis. ► Comparisons of embedded correlated wavefunction models are given. ► Electrostatic embedding combined with multireference wavefunctions most accurate. ► For delocalized excitations, Green's function methods superior, though much more expensive. ► Embedded correlated wavefunctions best for local excited states.